title: The molecular basis for UV vision in birds: spectral characteristics, cDNA sequence and retinal localization of the UV-sensitive visual pigment of the budgerigar (Melopsittacus undulatus).
abstract: Microspectrophotometric (msp) studies have shown that the colour-vision system of many bird species is based on four pigments with absorption peaks in the red, green, blue and UV regions of the spectrum. The existence of a fourth pigment (UV) is the major difference between the trichromacy of humans and the tetrachromacy of such birds, and recent studies have shown that it may play a determining role in such diverse aspects of behaviour as mate selection and detection of food. Avian visual pigments are composed of an opsin protein covalently bound via a Schiff-base linkage to the chromophore 11-cis-retinal. Here we report the cDNA sequence of a UV opsin isolated from an avian species, Melopsittacus undulatus (budgerigar or small parakeet). This sequence has been expressed using the recombinant baculovirus system; the pigment generated from the expressed protein on addition of 11-cis-retinal yielded an absorption spectrum typical of a UV photopigment, with lambdamax 365+/-3 nm. This is the first UV opsin from an avian species to be sequenced and expressed in a heterologous system. In situ hybridization of this sequence to budgerigar retinas selectively labelled a sub-set of UV cones, representing approx. 9% of the total cone population, that are distributed in a semi-regular pattern across the entire retina.
authors.affiliation: Department of Molecular Genetics, Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, U.K.
authors.forename: S E
authors.initials: SE
authors.lastname: Wilkie
authors.forename: P M
authors.initials: PM
authors.lastname: Vissers
authors.forename: D
authors.initials: D
authors.lastname: Das
authors.forename: W J
authors.initials: WJ
authors.lastname: Degrip
authors.forename: J K
authors.initials: JK
authors.lastname: Bowmaker
authors.forename: D M
authors.initials: DM
authors.lastname: Hunt
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D005796:Genes; D017403:In Situ Hybridization; D008565:Membrane Proteins / Q000737:chemistry; D008969:Molecular Sequence Data; D010240:Parakeets / Q000502:physiology*; D010802:Phylogeny; D011994:Recombinant Proteins; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D017299:Rod Opsins / Q000502:physiology*; D013057:Spectrum Analysis; D014466:Ultraviolet Rays; D014785:Vision, Ocular / Q000502:physiology*
chemical_list: D018076:DNA, Complementary; D008565:Membrane Proteins; D011994:Recombinant Proteins; D017299:Rod Opsins